Micropollutants in urban drainage systems: inappropriate sam- pling can flush data quality down the drain

After a decade of intensive research on residues of pharmaceuticals, personal care products and illicit drugs there is now a consensus that sewage treatment plants (STPs) are the primary entry route of these micropollutants into the aquatic environment. Analytical methods have become more sophisticated and the published values often reflect a fair level of confidence and accuracy of pollutant concentrations. However, the understanding of fate and removal efficiencies in STPs for numerous compounds is impeded by the wide variation of published values. In this study, we demonstrate that samples from STP influents, used to quantify removal efficiencies, can be subject to sampling artifacts if a careful systems analysis is not performed beforehand to determine the appropriate sampling mode and frequency. To this aim we carried out specifically-tailored sewer monitoring campaigns and a comprehensive literature review. The results from our field campaign show that sampling artifacts can range from “insignificant” to “100% or more”, even in 24-hr composite samples. The literature review reveals that 29 recent studies (January 2010 until March 2011) have analyzed raw wastewater samples for micropollutants: over 95% of all studies do not provide sufficient evidence in the final publication to assess the reliability of their results.